Supplementary Table 1. Data for individual females tested in insectary host preference tests. Data are the number of eggs laid on menispermifolia and P. vitifolia during the course of the trial.

a) cydno

Individual P. menispermifolia P. vitifolia 109 5 13 110 1 32 163 13 10 167 14 16 168a 11 3 c84 13 13 c94 7 11 1183 9 3 1084 1 17 c70 20 17 c72 25 24 c71 8 7 c99 8 3

b)

Individual P. menispermifolia P. vitifolia 15 26 0 16 37 0 17 18 0 31 16 0 32 5 0 33 33 0 34 25 0 35 9 0 40 19 0 49 20 0 50 19 0 51 2 0 52 36 0 53 25 0 56 23 0 57 11 0 58 12 0 59 8 0 90 17 0 92 25 0 93 13 0 111 5 0

c) First generation hybrids

Individual P. menispermifolia P. vitifolia 4 16 3 5 28 2 7 0 0 10 19 0 11 23 11 20 19 15 21 0 0 116 50 0 126 9 0 132 13 0 134 3 0 155 2 0 205 0 0 206 3 0 210 3 0 215 0 0 220 0 0 229 0 0 232 0 0 a 26 0

d) Backcross to H. melpomene

Individual P. menispermifolia P. vitifolia 88 29 0 119a 52 0 124 19 0 125 21 0 136 18 0 168 16 0 175 24 0 183 10 0 228 49 0 236 18 0 240 31 0 248 20 0 251 20 0 283 19 0 290 0 0 291 0 0 300 31 0 349 22 0

e) Backcross to H. cydno (including brood and colour pattern genotypes)

Individual Brood B locus Yb locus Ac locus P. menispermifolia P. vitifolia 253 C10 bb YbYb Acac 0 0 254 C10 bb NA acac 0 0 255 C10 Bb YbYb Acac 0 0 263 C10 bb YbYb Acac 0 0 267 C8 Bb Ybyb acac 22 7 275 C8 Bb YbYb acac 18 11 286 C10 bb YbYb Acac 18 6 287 C8 bb Ybyb acac 24 5 293 C8 bb NA Acac 0 0 296 C11 bb Ybyb Acac 0 0 305 C8 Bb YbYb Acac 0 0 307 C14 Bb Ybyb acac 5 5 312 C8 bb YbYb Acac 0 0 314 C11 bb YbYb Acac 17 0 320 C8 bb YbYb Acac 14 0 321 C8 Bb Ybyb acac 8 2 323 C14 Bb YbYb acac 22 13 326 C8 bb Ybyb Acac 0 0 326a C8 Bb Ybyb acac 25 14 330 C8 Bb YbYb Acac 0 0 374 C18 bb Ybyb Acac 5 4 375 C18 Bb Ybyb acac 23 15 376 C18 bb Ybyb acac 0 0 378 C8 bb Ybyb Acac 0 0 382 C8 bb YbYb acac 24 9 383 C8 bb YbYb acac 0 0 393 C18 Bb YbYb acac 0 0 397 C10 bb Ybyb acac 30 4 411 C10 Bb YbYb acac 0 0 423 C10 Bb YbYb Acac 23 0 427 C18 bb Ybyb Acac 0 0 430 C18 bb YbYb Acac 0 0 444 C18 bb NA Acac 0 0 454 C18 bb Ybyb acac 0 0 465 C18 bb Ybyb acac 21 0 456 C18 bb YbYb Acac 0 0 471 C10 bb YbYb acac 0 0 481 C18 Bb YbYb Acac 0 0 484 C18 Bb Ybyb Acac 27 0 487 C21 Bb YbYb acac 9 1 542 C24 Bb Ybyb acac 21 0 2012_166 E2 Bb YbYb acac 0 0 2012_182 E4 bb Ybyb Acac 0 0 2012_201 E5 Bb YbYb Acac 0 0 2013_596 H5 bb YbYb Acac 30 9 2013_607 H5 Bb YbYb Acac 5 2

Supplementary figure 1. The phenotypes of Heliconius melpomene (left), H. cydno (right), and a heterozygote (middle) at the loci studied here: i) red forewing band B locus, ii) the anterior part of the white forewing hourglass Ac locus, iii) the yellow hindwing bar Yb locus. The B and Ac loci have dominant alleles in H. melpomene; heterozygotes can only be distinguished in the backcross to H. cydno. The Yb locus is partially dominant so that heterozygotes can be distinguished in both backcrosses. In each pair of wings the lower surface is shown to the left and the upper surface on the right. Colour pattern loci genotypes are shown below each butterfly.

Supplementary Figure 2. Inheritance of sex-linked (W and Z) and autosomal (A) alleles in the crosses used to explore host acceptance in Heliconius cydno and H. melpomene. White boxes represent alleles inherited from H. cydno and red boxes alleles from H. melpomene. Note that females are the heterogametic sex in the .